DAS28 is a measure based on assessment of 28 joints for tenderness and swelling (tender and swollen joint counts). Disease Activity Score 28-C reactive protein (DAS28-CRP) is derived using differential weighting given to 4 components: tender joint count (range: 0-28), swollen joint count (range: 0-28), patient global assessment (recorded on a visual analog scale \[VAS\] scale of 0-100 mm), and CRP (milligram per liter). DAS28-CRP score ranges from 0 to 9.4. The lower the DAS28-CRP score is, the better the participant has response (remission = score\<2.6, low disease activity = score≤3.2). A negative value in change from BL indicates an improvement. Mixed Model Repeated Measures was used for statistical analysis, which used the change from BL of DAS28-CRP as an outcome and treatment, scheduled study visit, BL value of DAS28-CRP, treatment by visit interaction and BL by visit interaction as fixed effects. The model used the unstructured covariance matrix.

The SDAI is a continuous composite measure derived from components of the American College of Rheumatology (ACR) Core Dataset.The SDAI was calculated using the following formula: SDAI = Tender / Painful Joint Count(TJC) (using 28 joints) + Swollen Joint Count (SJC) (using 28 joints) + Patient Global Assessment of Arthritis (PtGA) (0-10 cm scale) + Physician's Global Assessment of Arthritis (PhGA) (0-10 cm scale) + high sensitivity C-reactive protein (hsCRP) (mg/dL). SDAI total score= 0-86. SDAI \<=3.3 indicates disease remission, \>3.4 to 11 = low disease activity, \>11 to 26 = moderate disease activity, and \>26 = high disease activity. The primary analysis utilized a Bayesian ANCOVA model with an informative placebo prior distribution with borrowing from tofacitinib historical placebo data. The confidence interval was credible interval in this statistical analysis. The efficacy endpoint for the tofatinicib arm was an exploratory endpoint and neither primary nor secondary endpoints.